The present invention relates to a composition for removing a polysulfide coating (sealant) from a metallic surface. More particularly, the instant invention concerns a composition adapted for use in stripping or removing a polysulfide basecoat from a metallic surface which composition comprises a chlorinated solvent and at least one activator selected from the group consisting of lower alkyl phosphite and aryl phosphine. The polysulfide basecoat may have associated therewith a polyurethane topcoat.
For sometime now, it has become a practice to use a polysulfide sealant material as a corrosion resistant basecoat for paint systems on numerous types of aircraft. Because of its resiliency, paints containing such a sealant have greatly improved the corrosion resistance of metallic parts and components. In practice, the complete finish may include a polyurethane topcoat with or without an epoxy primer between the urethane and polysulfide. Removing paint from an aircraft on a periodic basis is required for inspection and maintenance. Removal of a paint system having a polysulfide basecoat is a very difficult task. Prior to the instant invention, it has been necessary to spend a great deal of time and effort scraping, brushing and sanding to remove such a basecoat. This is time consuming and can result in excessive damage to aircraft skins. As a result, the polysulfide basecoat may not be completely removed from many of the aircraft currently being overhauled and this interferes with proper inspection procedures.
One commonly employed system for removing polysulfide coatings from a metallic surface utilizes various mercaptans. However, while this system performs adequately with respect to the physical removal of the polysulfide coating, it suffers from certain undesirable side effects. For example such systems are generally corrosive to aircraft metals, particularly cadmium plated steel which is is used extensively on jet aircraft. In addition, because of the corrosiveness with respect to cadmium plated high strength steel, such systems often cause severe hydrogen embrittlement. Another problem associated with mercaptan usage is that such compounds exhibit a very offensive odor. From an economic standpoint, these systems suffer due to their poor shelf life. Another serious problem associated with mercaptan containing systems is that the ingredients cause severe pollution problems.
Accordingly, it is the principal object of this invention to provide a composition and method for removing or stripping a polysulfide basecoating, which may be overcoated with a topcoating of urethane, from a metallic surface or substrate while avoiding or at least minimizing the problems associated with prior art expedients for removing such coatings.
These and other objects of the instant invention will become apparent to those skilled in the art from a reading of the following specification and claims.